I. Technical Field
The present invention relates to a tablet suitable for sealing an exhaust pipe and an exhaust pipe integrated with a tablet, and more particularly, to a tablet suitable for sealing an exhaust pipe of a plasma display panel (hereinafter, referred to as “PDP”), various types of a field emission display (hereinafter, referred to as “FED”), or a vacuum fluorescent display (hereinafter, referred to as “VFD”) and an exhaust pipe integrated with a tablet.
II. Description of the Related Art
A composite material containing a glass and a refractory filler is generally used as a sealing material. The sealing material is more excellent in chemical durability and heat resistance, and is more suitable for ensuring airtightness than an organic adhesive material.
The sealing material is required to have properties such as mechanical strength, flowability, electrical insulation, and low-melting property, depending upon the application. In particular, in the case of using the sealing material in a PDP or the like, it is required that the sealing material can be sealed at a temperature (for example, 500° C. or less) at which the fluorescent property of a fluorescent substance is not degraded. Hitherto, lead-borate glass, which satisfies the properties, has been widely used (see JP 63-315536 A).
However, environmental problems concerning PbO contained in the lead-borate glass have been pointed out recently. Therefore, it is desired that the lead-borate glass be replaced by lead-free glass, and various lead-free glasses have been developed currently. In particular, bismuth-based glass (Bi2O3-B2O3-based glass) described in JP 06-24797 A or the like is substantially similar to the lead-borate glass in various properties such as a thermal expansion coefficient. Therefore, the bismuth-based glass is expected as an alternative candidate for the lead-borate glass.
Meanwhile, in the case of the PDP or the like, the inside of a device is exhausted and then filled with noble gas, and hence it is necessary to attach an exhaust pipe. Such the exhaust pipe is attached so that the position of an exhaust hole provided in a glass substrate of the PDP is matched with an opening of a front end portion of the exhaust pipe.
In general, in attaching the exhaust pipe, a tablet (also, referred to as “press frit” or the like) obtained by molding a sealing material is used. when the tablet is used, the alignment between the exhaust hole of the glass substrate and the opening of the front end portion of the exhaust pipe becomes easy, and the exhaust pipe can be attached to the glass substrate stably. Further, when the tablet is softened, the exhaust pipe can be sealed to the glass substrate.